Prior Art devices of this type have relied on a variety of different configurations all of which are aimed at the same end result of high speed incremental chopping of strip scrap. The reader is referred to, example, U.S. Pat. No. 2,125,939, U.S. Pat. No. 3,084,582, U.S. Pat. No. 3,799,020, and U.S. Pat. No. 4,858,506 (Buta).
In U.S. Pat. No. 2,125,939, a rotary shear knife is disclosed that uses raked cutting edges on cutting knives positioned on drums so that they register as opposing knives when brought together to shear the material. Each of the knives cutting edges are of an involuted curved configuration so that the cut will be square in relation to the strip being cut.
U.S. Pat. No. 3,084,582 discloses a rotatable shearing blade device for progressive transverse cutting using a pair of blades each mounted on a separate spindle with a gear tooth mechanism inner-connecting them. Each blade is held by bolts and springs for relative adjustment. Each blade has only one cutting edge for engagement against the material to be cut.
In U.S. Pat. No. 3,799,020 a scrap chopper is shown having a fixed station knife and a multiple bladed rotary arbor aligned for cutting registration therewith.
In U.S. Pat. No. 4,858,506 a scrap chopper is shown have a dual arbor with at least one pair of blades which have been mounted in an angular, transverse relationship to the arbor. The blades themselves are defined as being in a symmetrical, multi-sided configuration wherein a front and back surface of the blade is curved on a constant radius to provide four curved cutting surfaces. As such, each side edge of the blade provides an identical cutting surface and four individual cutting edges can be selected by inverting and/or rotation of the blade. The blade is adapted to be held within a curved slot provided in the arbor, and a sound pad of variable thickness is added to assist in fitting of the blade within the slot.
Due to the arbor and blade design configurations a unique cutting ability is provided on matched counter rotation of the arbors to bring a pair of oppositely disposed blades, and their associated cutting edges, into the progressive shearing relationship which is required for cutting strip scrap material at high speed.
While this configuration has proved to be acceptable for use, precise and immovable fitting of the curved blade, within the curved blade well of the arbor, has proven to be difficult and time consuming. As such, it would be preferred to provide improved blade and arbor designs and configurations which can be more easily changed or replaced.
It is also known in the prior art that, for a dual arbor configuration, an elliptical radius on the blade provides optimal contact across the entire width of the blade. However, milling the blade to an elliptical configuration can be complex, can be difficult, and typically is not worth the additional expense involved.
As previously mentioned, in U.S. Pat. No. 4,858,506, the blade surface has a single constant radius, and the constant radius is selected in order to provide a reasonably close fit to the elliptical shape design. While this approach is acceptable for use, it would be desirable to provide a simple blade design which more closely matches the optimal elliptical design. Further, this should be achieved without significantly increasing the complexity of the blade milling operation.